Renegade Ops

Note: this can be done in co-op; thanks to 'ShootZombies' for this information.

Hardcore mode certainly is tough; much tougher than normal.
Fortunately, there are some things which make it much easier. Mainly, the upgrades you choose.

UPGRADES
keep in mind that when you unlock an upgrade, you don't necessarily have it equipped (showing a green tick icon).

I would suggest selecting:
- Auto reload
- Efficiency - Elite

I'd say Auto reload is essential. I found my play-style changed completely, using rockets willy-nilly and taking out enemies far quicker. Even if you use all your secondary ammo, you'll usually have regained it by the next fight.

Efficiency elite just makes your character's ability occur more often; which is very useful.

Then two of your own choosing, most likely another Tactical one i.e. Static Shock or guarded repair and a defense. Use your own best judgement on these two.

GENERAL TIPS
Enemies shoot where they think you will be. For that reason, try to engage from a distance. This gives you more time to avoid shots coming your way. One exception is the large tanks; try circling them instead.

Missile launchers are very dangerous; you want to move in circles. Once you commit to one direction, don't change direction, as you'll probably go straight into any chasing missiles.

Your bullets can hit enemies just off the edge of the screen and they won't shoot back. Use this if you need to.

Don't be afraid to use your secondary ammo, you get given a fair amount all the time.

Some levels have crates to allow you become a gunship. Personally, I'd prefer not to use these, as it's turning speed is very slow and you lose your ability. You do gain faster movement though...your choice!

Try a couple of the characters on normal, but try to decide on one to get used to. In the heat of battle you don't want to try use shield while playing as Diz, for example.

SPECIFIC LEVELS / AREAS
Mission 1 & 2
these aren't too bad and it should be possible to complete with a level 10 character or similar

Mission 3
Once you get to the stage of picking up relics, try not to go too out of your way. Time is of the essence.
While awaiting the phoenix gunship, drive through any nearby buildings to give yourself some clear space.

Mission 7
This is actually a bit easier, since you have an ally. Whenever you're feeling the strain, stay near the other tank.

Mission 9
This is a big step up. I had to attempt it about half a dozen times. I recommend using Armand, as the enclosed space means rockets still hurt that miss (hitting walls); his shield helps here. Also, the fights are very spread out, meaning Guarded repair is useful.
There's a mining area with a Juggernaut. Just race through here, no need to kill him. It's too risky.

FINAL BOSS
Inferno himself doesn't attack too aggressively, so try to keep your distance - his flame attacks are very dangerous. Also, his rockets are easier to dodge the further away you are. Remember, you can hit him even when he's just off the screen edge. The attacking gunships are annoying, but they do drop health. The biggest dangers are the mortars, remember to change directions.
Focus any secondary ammo on Inferno.

Best of luck; if there's anything I should try clear up message me or comment. In case you're finding any other places tricky, let me know too and I'll try add something about it too.

This is just to let you know, YES it can be done in Co-op. Only the Achievements that say 'Single Player' are single player.

I did the whole game Co-op on Hardcore and the Achievement unlocked. Most of the levels only took 1 or 2 tries to complete with varying amounts of Co-op'ers 2-4 players. So all the other solutions tips will help you up to Mission 9.

Mission 9 is a REAL PAIN IN THE ASS... This took me OVER 20 tries to finally complete on Hardcore. I tried both solo and Co-op and it just pissed me off no end. There are less enemies in solo but the way they're spaced out there's always some annoying rocket machine hitting you in the butt when you're focused on a tank.

I finally did it this way...

4 Player Co-op. 2 randoms, a friend and me.
3 of us were 'Diz' the EMP character and the 4th was the air strike character. I reckon 4 EMP'ers would work even better.
Everyone was obviously fully upgraded, I used 2 slots for EMP cooldowns and the other 2 for EMP Radius and Duration. So all my eggs were in one basket so I could use EMP frequently :)
Between us EMP's were going off all the time which meant enemies were hardly able to fight back. All the areas where enemies were spaced out and would normally kill me in single player were neutered by the other 2 EMP players who would EMP the other side of an area. Having more than 2 EMP'ers meant Every Area could be completely controlled and that someone always had a recharged EMP at hand ready to use. This technique was really useful during the final elevator ride.
(We also just drove past the Juggernaught. Don't waste time with him as he can't chase you :)

Doing it this way I not only completed the level but I completed the level without losing any lives and with a skill rank of Alien...!!! Shame that Achievement has to be done single player :)

So do it Co-op with 4 Fully upgraded EMP'ers and you can laugh in the face of Mission 9.

Thanks.

The only real guide that would serve this achievement is a how to on playing in hardcore difficulty.

Just try and learn to dodge rockets, run circles around tanks and keep a high damage streak and you should be fine.

If you need to, there's no shame in digging into those Defensive upgrades! Try maxxing out a character on Normal difficulty - this will give you lots of upgrades to play with and you'll have enough experience to play well.

If you're having trouble with Inferno on level 9, just remember that once his weak point is open it only takes 6 rockets to bring him down - or even just use Armand's rebound to utilize his rockets against him.

Most is already covered in the other guides but I really think I should make a guide and let everyone know something important. For tips and help, read the other guides.

If you do this achievement in multiplayer and one player gets a game over. Do not continue on the next levels until all players have at least survived that mission one time.

We were 4 players, one of us got a game over on level 4 and after that this player never got another game over. However he did not get the achievement. And after we replayed level 4 for him, he still did not get the achievement. Meaning that if you skip a level the others do not count.

We let him create a lobby and it only said he could pick up to the 4th level were he had gotten a game over.

ONE THING U GOTTA BE AWARE OF :
surprisingly neither me or my buds having the same issue have ever hear or read about this:
i´m pretty sure u have to finish all missions in the correct order - u can do some in singleplayer and some in coop but if u - for example - do mission 1 and 2 in SP and then finish 4-9 in coop it won´t count and you still need to finish 3-9 to unlock the cheevo !
start from the last mission that u can choose on hardcore in SP or when hosting coop....we wasted alot of time by not doing it like this